请教，LDO设计中，调整管栅极电压怎样可以降低？

xuyanyan141

我最近在设计ＬＤＯ，把调整管作为运放第三级，放进去仿真调试。可是发现调整管栅极电压居高不下，该如何降低调整管栅极的电压，也就是误差放大器第二级输出电压呢？

xuyanyan141

实在是搞不懂了

shiunger

Could you show your schematic?

xuyanyan141

回复 3# shiunger


    不知能不能看清楚

xuyanyan141

回复 3# shiunger


    谢谢啦 你真热心

shiunger

Why did you use common-source at your 3rd-stage?

goodsilicon

这时候有负载吗，加上负载这点电压就下来了，－－假设你的电路正常工作的话。

goodsilicon

Why did you use common-source at your 3rd-stage?
shiunger 发表于 2010-11-12 14:20

                               
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why not??

shiunger

Yes, we could certainly use common-source at the output stage.
I just wondered why did you use a high impedance output stage to drive a current load.
I assume the current load is low impedance.
Am I right?
Thanks!

why not??
goodsilicon 发表于 2010-11-12 14:27

                               
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goodsilicon

Yes, we could certainly use common-source at the output stage.
I just wondered why did you use a hi ...
shiunger 发表于 2010-11-12 15:04

                               
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[size=14.1667px][size=14.1667px]Unfortunately, you are wrong.
[size=14.1667px]since it is a closed loop, the output [size=14.1667px]impedance is low at the output, at least at low frequency. So, it can work as a voltage source to drive a low [size=14.1667px]impedance[size=14.1667px]. [size=14.1667px] Thanks!